The WalKR System Controls Major Staphylococcal Virulence Genes and Is Involved in Triggering the Host Inflammatory Response

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>The WalKR two-component system is essential for the viability of<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Staphylococcus aureus</jats:named-content>, playing a central role in controlling cell wall metabolism. We produced a constitutively active form of WalR in<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">S. aureus</jats:named-content>through a phosphomimetic amino acid replacement (WalR<jats:sup>c</jats:sup>, D55E). The strain displayed significantly increased biofilm formation and alpha-hemolytic activity. Transcriptome analysis was used to determine the full extent of the WalKR regulon, revealing positive regulation of major virulence genes involved in host matrix interactions (<jats:italic>efb</jats:italic>,<jats:italic>emp</jats:italic>,<jats:italic>fnbA</jats:italic>, and<jats:italic>fnbB</jats:italic>), cytolysis (<jats:italic>hlgACB</jats:italic>,<jats:italic>hla</jats:italic>, and<jats:italic>hlb</jats:italic>), and innate immune defense evasion (<jats:italic>scn</jats:italic>,<jats:italic>chp</jats:italic>, and<jats:italic>sbi</jats:italic>), through activation of the SaeSR two-component system. The impact on pathogenesis of varying cell envelope dynamics was studied using a murine infection model, showing that strains producing constitutively active WalR<jats:sup>c</jats:sup>are strongly diminished in their virulence due to early triggering of the host inflammatory response associated with higher levels of released peptidoglycan fragments. Indeed, neutrophil recruitment and proinflammatory cytokine production were significantly increased when the constitutively active<jats:italic>walR</jats:italic><jats:sup>c</jats:sup>allele was expressed, leading to enhanced bacterial clearance. Taken together, our results indicate that WalKR play an important role in virulence and eliciting the host inflammatory response by controlling autolytic activity.</jats:p>

Dual Targeting of Cell Wall Precursors by Teixobactin Leads to Cell Lysis

“…Among these systems, WalKR is essential for viability and is involved in cell wall metabolism. A strain expressing a constitutively active form of WalR displays upregulated atl transcription (40). GraRS is a well-studied system which regulates the resistance to cationic antimicrobial peptides.…”

Two-component signal transduction systems in oral bacteria

“…P-VicR induces expression of PcsB and other murein hydrolases, but NP-VicR directly represses fabT , encoding a repressor of genes for fatty acid biosynthesis and, in turn, upregulates membrane synthesis [137]. Phosphatase activity has also been shown in the S. aureus VicK, also known as WalK [138]. Therefore, VicRK TCS apparently switches functions affecting the homeostasis of the cell envelope both by its kinase and phosphatase activities, and, in turn, by balancing the levels of P-VicR and NP-VicR.…”

“…There is evidence that VicRK interacts with other regulatory circuits involved in cell-envelope homeostasis during challenges with a range of environmental stresses [107,138,139]. Some of the regulators found to interact or to cooperate with regulation of VicRK-gene targets include the orphan regulator CovR of S. mutans [107,117] and the TCS SaeSR of S. aureus [138]. In S. mutans , vicRK expression seems to be also indirectly induced by the TCS LiaSR [135], a TCS that regulates responses to cell-envelope stresses [140].…”

“…These findings indicate that VicR/CovR cooperate to more precisely coordinate functions of cell division with biofilm formation and evasion of host immunity, two essential functions for S. mutans persistence in oral niches. In S. aureus , VicRK Sau interacts with the SaeRS TCS to upregulate expression genes with similar functions, and so it is possible that VicRK systems may cross-talk with other TCSs involved in bacterial evasion of host immunity [138]. Direct approaches to establish the molecular mechanisms underlying these potential cross-talks remain to be performed.…”

Structural basis of PcsB-mediated cell separation in Streptococcus pneumoniae

“…During the last decade it has become clear that a twocomponent regulatory system termed WalKR (also known as VicKR and YycGF) controls PG metabolism in low G þ C Grampositive bacteria 2 . Analysis of the WalKR regulons of Bacillus subtilis and Staphylococcus aureus have revealed their role in the control of the expression of a number of PG hydrolases, some of which are involved in the separation of daughter cells 3,4 . Similarly, genes encoding several putative and proven PG hydrolases are part of the pneumococcal WalKR regulon 5,6 .…”